1. Field of the Invention
The present invention relates to a charging member, a process cartridge, and an electrophotographic apparatus.
2. Description of the Related Art
In an electrophotographic image forming apparatus (hereinafter referred to as “electrophotographic apparatus”), a roller-shaped charging member used for contact charging of an electrophotographic photosensitive member serving as a body to be charged generally has an elastic layer so as to ensure a sufficient nip width with respect to the photosensitive member. It is to be noted that, hereinafter, the electrophotographic photosensitive member is also referred to as “photosensitive member”, and the charging member is also referred to as “charging roller”.
In recent years, there has been a demand for increases in speed and durability, and enhancement of image quality, of an electrophotographic apparatus, and in a printer of a medium speed or more requiring high-speed drive, the vibration of a photosensitive member increases along with high-speed drive. The vibration of the photosensitive member causes the contact between a charging roller and the photosensitive member to be unstable, and hence the charging of the surface of the photosensitive member by the charging roller becomes non-uniform, with the result that an electrophotographic image with lateral streak-like uneven image density (hereinafter sometimes referred to as “banding image”) is formed in some cases.
As a technique of suppressing the influence on the charging roller by the vibration of the photosensitive member, Japanese Patent Application Laid-Open No. 2004-279578 discloses a charging roller using an electroconductive foam elastic layer. Further, Japanese Patent Application Laid-Open No. 2009-134310 discloses an electrophotographic member containing an inorganic balloon such as a silica balloon or a carbon balloon in an elastic layer.